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Plant Problems

By: Dr Gareth Evans - Updated: 8 Jul 2018 | comments*Discuss
Plants Pond Pests Problems Disease

A well planted pond makes a striking centre-piece in any garden. Although in general water plants tend to be less bothered by pests and disease than their dry-land counterparts, there are still a variety of problems which can affect them.

Keeping your aquatic plants in good health calls for a little vigilance. If you know the tell-tale signs to look out for – and act quickly – you should be able to make sure that your pond is always looking its best and stays an attractive garden feature.

Insect Pests

When it comes to pests, a very large proportion always seem to be insects – and the water garden is certainly no exception!

The 2.5cm (1 inch) long caterpillars of the China Mark Moth, for instance, emerge from eggs laid on the leaves of various kinds of water plants towards the end of the summer. These cream-coloured larvae, with their characteristic brown heads, bite oval-shaped holes in the foliage, fixing the pieces they remove together with silk to make a floating shelter where they feed on other aquatic plants, grow and ultimately pupate.

Although they are seldom a major problem, they can cause a fair bit of damage in small ponds – so, however fascinating you find their natural engineering skills, it’s best to remove any of their floating cases that you come across.

The Leaf-Miner Midge is another insect pest which, though not especially common, can be highly destructive to a wide range of water plants. The midge maggots themselves are small, thin and almost transparent, making them very difficult to see but, their presence is very easy to spot, especially if the attack is severe. Eating their way quickly through the soft tissues between the veins, the larvae rapidly produce skeletonised leaves in their wake.

There isn’t a treatment as such; all you can really do to improve things is pick off any affected leaves and destroy them.

Water Lilies

Of all pond plants, water lilies are probably the most commonly affected by pests and problems – some of which are entirely their own.

The Water Lily Beetle, for example, can cause major damage to their foliage, laying eggs that hatch into voracious black grubs with yellow undersides, which then eat their way through the leaves, causing big holes to appear. The damage they do eventually causes the leaf to shrivel and die, and if it is not removed, it will ultimately start to rot.

The only effective treatment is to ruthlessly remove and destroy the worst affected leaves and wash the remainder with a garden hose – and since this small brown beetle can lay three or even four clutches of eggs over the summer, you may have to do this more than once.

Fortunately this pest is only an occasional problem in small garden ponds, since it tends to prefer larger expanses of water, but if you are unlucky enough to find evidence of them, quick action will be necessary to save your plants.

Water Lily Aphids are another pest to be on the look-out for, especially during spells of hot, dry weather, when they may appear in huge numbers on the leaves, stems and buds. Although they are individually very small – much the same size as the more well-known vegetable black-fly – a large population feeding off your plants can cause weakened growth and distorted or absent flowers. Treatment again involves washing them off with a hose; they’ll make a tasty snack for any fish or wildlife in the pond.

Crown Rot

One of the most serious problems to affect water lilies, however, is not an insect, but a fungal disease related to potato blight – Water Lily Crown Rot – which can decimate a pond’s lilies if it is allowed to take hold. If you’re buying water lilies for your pond, it’s vital to inspect them carefully for any signs of infection, the easiest symptom to recognise being a black, soft spot on the lily’s rhizome.

The leaves of infected lilies will turn yellow and then break away from crown, which gradually blackens and eventually becomes foul-smelling; any affected plant needs to be removed and destroyed as soon as possible to contain the infection – which may spread to all of the lilies if left to run its course.

Fortunately, aquatic plants seem to be very resilient on the whole – which is a good job, given the obvious problems that trying to use any kind of pesticide in a pond would bring! Knowing what to look out for is half the battle and if you act swiftly to remove any affected foliage or plants as necessary, looking after your water garden shouldn’t give you too many problems.

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[Add a Comment]
I have elephant ear plant but I have recently noticed the roots have white tentacle like things hanging off of them. Two of my koi carp have also died in the last week and one is looking ill. The water has also become strangely murky. Is this purely coincidental, or are these plants infected or something else.
Merar - 8-Jul-18 @ 8:55 AM
Dot - Your Question:
Tall reeds growing strongly in pond have what looks like blackfly. How can you treat please without damaging the fish?

Our Response:
It's probably best to take a picture of the pests and take it your garden centre for advice on which fish-friendly treatment to use.
PondExpert - 11-May-17 @ 2:08 PM
Tall reeds growing strongly in pond have what looks like blackfly. How can you treat please without damaging the fish?
Dot - 10-May-17 @ 12:01 PM
One of my goldfish appears to spend most of its time nose down but, if disturbed, is quite animated.Any comment would be most welcome.
Widower - 5-Jun-13 @ 9:22 AM
my waterlily has things that look like chunks of wet bread in it very often, n gets quite mucky looking frothy jellyish bubbles on the surface as well!! i have NO idea what this could be, n wonder if anyone has any ideas about what it is n how i can treat it??(preferably organically) please? n thanks in advance!!
retro-grrl - 13-Apr-13 @ 4:49 PM
My lilly pad leaves are being eaten. There are whitishjelly like lavae? about inch long on the underside of the leaves. some of the Lilly flowers are also being eaten. Anyone advise?
Todd - 13-Aug-12 @ 6:47 PM
Pond plant problems; I have water lily's with what looks like grains of pepper all over their leaves, top and bottom. It's not fungus, so it must be some kind of eggs? What do you suggest to get rid of these, without harmful insecticides?
Ang - 27-Jul-12 @ 8:17 PM
Dear Chef, the tubular jelly stuck under leaves is almost certainly pond snail eggs. I looked this up on Google last year when I had lots. Jennifer
Jennifer - 7-Jun-12 @ 2:47 PM
I am very curios as to what are the clear jelly like tubes 1 1/2 cm in length that are attached to plants and other fixed items in my pond. Are they the lava of leeches, snails or what? Also, I often find little white balls attached to weed, is this newt eggs? Can you help? Many Thanks Chef
Chef - 21-May-12 @ 8:11 PM
For the past several years my water lilies have given me a wonderful show , but this year although they have bloomed quiet well the pads are coming to the surface folded in half, also the blooms are not as large or as abundant as in the past, I would be most gratefull if you could offer any advice on my problems.
Michael Murphy - 2-Aug-11 @ 6:50 PM
We have a pond that we have pretty much left to nature, it's really a fish pond as it's around 3ft deep in the centre and doesnt have much in the way of marginal areas however it has lots of oxygenators in it and water hawthorn and was teaming with water boatman, greater diving beatles, shrimps, pond skators and water fleas etc. This year we decided to take some frogspawn from a friends pond as he has a carp that eats most of the spawn in his pond. The resulting tadpoles have done amazingly well and most have now turned into tiny frogs and are thriving. I have noticed however that i no longer see ANY water boatmen and diving beatles in the pond and in fact the only life i see apart from the tadpoles and frogs is snails, pond skators and the very occasional shrimp. I really don't understand what has happened to the beatles, i keep reading that the greater diving betales in both larva and adult form eat tadpoles and should be thriving in there so what is going on ? Any suggestions as to where all our beatles have gone would be very welcome. Ben
collbe - 17-Jun-11 @ 9:09 PM
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